September 2010

September 18, 2010

A gigantic and deep low pressure south of New Zealand is generating large swells all along the coast of South Eastern Australia this morning. The low pressure, reported to be one of the largest depressions on the planet, is expected to create 17 metre waves around Tasmania.

Photographed this morning; Saturday 18th September at dawn. The waves are held up by a fresh offshore wind.

The waves combined with an early morning high tide are causing surges of water to surge in above the the normal tide levels.

Long lines of waves break in the early morning light.

An Australian Pelican contemplates the waves... I think he decided it too dangerous to be out there... maybe something to eat may get washed ashore...

September 01, 2010

One of the most recurring assumptions relating to over water
bird migration is that the vast expanse of the seas and oceans are devoid of
the visual landmarks we humans regard as necessary to find our way. Therefore
birds also would be unable to navigate visually and so they would therefore
have some super ability to navigate using the earth’s magnetic field and the
stars.

A Bar-tailed Godwit in flight. Like many birds their feathers provide a beautiful pattern. The pattern however may provide the means by which they navigate.

It’s not surprising really that we assume the seas are
featureless. Just about any map that we pick up depicts the oceans as empty
blue spaces between landmasses. Our history of navigation that was predominated
by ships reinforces this assumption. From the deck of a ship the sea all looks
pretty much the same.

Birds that fly over the oceans, funnily enough, have a
birds-eye-view and it’s a completely different perspective.

So lets pretend once again that we are flying our little
aeroplane from Alaska to New Zealand and somewhere out of sight but not far
away, E7 the magnificent Bar-tailed Godwit is doing the same.

High up above us an airliner is winging its way across the
Pacific using a state-of-the-art Flight Management System which gets its
navigation information from a combination of inertial navigation systems and
multiple GPS. For these pilots navigation is precise and reliable. Not
surprisingly nowadays, the pilots of these aircraft are largely oblivious to
the visual cues beneath them.

But up to the introduction of inertial navigation equipment
and GPS flight across the ocean was not so plane sailing, particularly in light
aircraft. By today’s standards pilots relied on navigation equipment that was
alarmingly crude.

Like E7, many of these flights crossed the Pacific Ocean
between North America and New Zealand. There were a small bunch of intrepid
aviators delivering small single and twin-engined light aircraft from their
manufacturers in the US whose efforts are largely unknown. They flew the long
non-stop flight between California and Hawaii and then island hopped the rest
of the way. Other small agricultural aircraft that were manufactured in New
Zealand went in the reverse direction.

Many light agricultural aircraft such as this DHC Beaver were flown both directions between the USA and New Zealand. They relied on basic navigation, luck and a sharp eye to avoid disappearing in the Pacific Ocean. Not all of them made it!

These small aircraft were almost always flown by a single
pilot crammed into his or her seat with every other bit of available space
taken up with extra fuel tanks. They had the most basic of navigation
equipment. The most they had was a chart with the great circle route plotted, a
compass and a blind faith that they would come within receiving range of a
radio beacon that could guide them in to their often small remote destinations.
Radio beacons that were often switched off, unserviceable or of such low power
that they had to be almost within sight of their destination before it would be
of any use. By necessity, those pilots learned techniques based on visual
observation of the sea and the clouds to help them find small atolls in the
middle of wide blue ocean where they needed to refuel and break their journeys.

If there is one thing that birds are very good at it is
their vision and observational abilities. The anatomy of birds’ eyes and the
light spectrum they can perceive is different to ours and that gives them
abilities we humans are unaware. Their whole lives are dependent on acute
eyesight and mental visual pictures of their world… for foraging, reproduction,
defence, avoiding crashing into things while flying… after all when you travel
at the speeds birds do their whole observation, processing and
manoeuvring systems need to be super fast and precise to avoid being eaten, to
dodge between trees, branches, buildings, fast moving cars, wind generators and
even to land on branch or telephone wire without crashing… and last but not
least, their vision is used for navigation. Not only are they seeing things
that we can’t see, but also they are recognising and using visual information
that we ignore or think is insignificant.

Australian Pelicans rest on a brackish coastal lake west ofDili in Timor Leste. Birds migration maybe seasonal or just in response to local conditions. When these birds were photographed in February 2008 Australia was in one of its worst droughts in recent history.

Surfboard riders flock to the islands of Indonesia. Along
the south west coasts of Bali and the island chains off Sumatra waves break on
the reefs and headlands with a consistent regularity that makes this beautiful
part of the world a surfer’s Mecca. Warm tropical seas, consistent surf and
cheap living… I’m packing now… and lots of interesting bird life.

The waves that surfers travel from all over the world to
surf on are not generated in Indonesia. They are born deep in the southern
oceans by the consistent gales in the roaring forties and fifties and travel
thousands of miles across the Indian Ocean before colliding with the coasts of
Indonesia. Similarly swells generated in the high latitudes travel across the
Pacific from both north and south.

Flying south from the bottom of New Zealand into the
southern ocean to oil rigs I have witnessed these giants of the sea. The swells
are long and large, deceptively ponderous and are never absent even on the rare calm days. These immensely stable swells contain millions of tons of
inertia and travel in consistent lines of constant direction that change little
as they travel. They are stable patterns that remain the same from year to
year. Although local winds and storms may produce a confusion of conflicting
sea patterns above, the underlying swells continue on unchanged beneath the
turmoil. From the air they are unfailingly discernible.

A Royal New Zealand Air Force Iroquois helicopter flying over the reef on the southern side of the Fijian island of Vitu Levu.An endless progression of swells that originate in the southern oceans breaks on the reef. Fiji, as well as a good birding destination is a consistently good surfing spot.

Having spent many hours flying above the oceans from the
tropics to the sub arctic, I observe these swell patterns regularly. Even a
glassy smooth tropical sea has long slightly darker lines that giving away
their presence. And because they are so consistent they provide a directional
matrix on the surface of the sea. Birds only need to measure their angle
against these lines and they have a consistent steering guide. And most
beneficially these swell patterns follow direct paths across the ocean.None of the problems, as discussed in
my earlier posts on navigation, regarding the vagaries of magnetic variation
and the complexity of calculating the compass directions required to maintain
great circle tracks exist. The swells are geographically orientated and have no
magnetic influences.

Birds use these visual grid lines to provide them with the
steering information as well as compensating for the effects of the wind. Many
birds, and the bar-tailed Godwit in particular have beautiful patterns on their
wings, tails and bodies, often consisting of bars and angled lines – hence
Bar-tailed Godwit. Observing these feather patterns on fellow birds at close
proximity with each other within the flock in relation to the swell lines may
well provide them the method of assessing the angle they need to maintain a
steady track as well as working out whether the wind is blowing them off track.

If we look back to our early aviation pioneers we can see
how some airborne navigators used the texture on the surface of the sea (and
the land) to help find how much they were drifting off track caused by the
wind. They had a simple yet effective doohickie called a drift sight. It was
basically a tube the navigator could look through vertically at the surface of
the sea. It had a series of parallel lines on a lens that could be rotated. The
navigator rotated the tube until the lines followed the texture of the surface
of the sea. The difference in angle between the lines and fore and aft axis of
the aircraft was the drift angle.

So birds, by using the barring patterns of their neighbours wings
and tails as reference lines, can judge not only the angle of the swells to
which they need to fly but also how much the winds is blowing them off track.
Using this information they know which heading to fly and to compensate for the
wind.

Black-tailed Godwits in Timor Leste. Like their cousins the Bar-tailed, these migrants also have distinctive wing and tail patterns.

Unlike the sun and stars, observing swell patterns are not
blocked out by cloud. And using their excellent night and UV vision, birds can
see the swell patterns just as well at night and possibly by using
phosphorescent footprints on the surface of the sea.

But, as discussed in previous posts; using steering
information such as swell patterns is dead reckoning and only part of the
navigation process. Birds still need position fixes to confirm they are going
in the right direction and to be able to correct for any errors that have crept
in. So what other features are observable on the so-called featureless oceans.
Well mostly there are clues on the clouds and sea surface itself.

Over the sea clouds tend to build up over land. Even a sand bank such as this one in the Timor Sea can provide sufficient day time heat to trigger a cumulonimbus storm cloud. At full development they can attain a height of 60,000 ft.

Now you may be forgiven for thinking that clouds are just
clouds and are just randomly scattered about the sky. Clouds are the result of
variations in the air itself; of humidity, temperatures and air currents, but
also highly influenced by the sea or land beneath them. They have form and
location that are dependent on such things as the topography and temperature of
the landmass or the temperature of the sea. They consequently have some
predictable and recognisable features. There is a line of clouds off the south
coast of Timor Leste that is in the same spot almost every day. A giant cumulonimbus
storm cloud that sits above Bathurst Island north of Darwin is so consistent that
it has a name… Hector! Clouds such as Hector congregate above islands generated
by the daytime heat from the land … huge towering clouds that reach fifty to
sixty thousand feet into the upper atmosphere. They are visible from huge
distances.

Not only are they visible during the day but also they glow
internally at night. Ferry pilots use clouds as beacons during the day and
night. Strange as it may sound the colour of the clouds also give reliable
clues as to whether or not there is land beneath them. And while clouds are
often associated with islands, it’s not always the case. We in our little
aeroplane and E7 looking at a line of clouds over the distance horizon may be confused
as to which ones are over land and which are over the sea. Clouds reflect the
surface beneath them. The reflection of the blue lagoon on the clouds above it are unmistakeable, as do clouds above a forested island
reflect the green of the trees.

And there is the visual texture of the sea surface itself
that gives those that are observant clues to fixed locations. Oceans currents
rise from hidden sub sea topography giving constant evidence
of the presence of undersea landmarks almost as if they were visible above the
surface of the sea. Between Fiji and New Zealand there is an almost continuous
deep trench and ocean mountain range. Such sub sea topography may provide more
orientation for birds to follow.

Looking at the flight paths that E7 took there is an evident
plan that minimizes the risks of getting lost. Pilots flying to small
islands used similar techniques… playing the odds. The pilot estimates the time at which he or she is expecting to get there. If
the island doesn’t appear as expected rather than keeping going and run out of
fuel and perish it is best to turn at right angles to the track and see if the island can be found. But which way does he or she turn?
Go the wrong way… perish again! So pilots would deliberately steer off track to
one side and if the island didn’t appear they would know which way to turn to
look.

By tracking south from Alaska, E7 would come across the wide
stretch of islands and reefs of the Hawaiian Archipelago that stretched across
her track from Midway Island to Hawaii itself. Picking up the visual cues of
the archipelago from a hundred miles or so away, she then turned southeast
towards Fiji. Between the Hawaiian Archipelago and Fiji identifiable landmarks
in the Central Pacific Basin, the Gilbert and Phoenix Islands become more
common. From Fiji south to New Zealand the Tongan and Kermadec Ridges would
guide her until sensing the northern tip of New Zealand she would turn towards
her final destination. All the time using the ocean swells as her steering guide.

No creature is born with a map hardwired into his or her
brain, birds included. Humans have the most advanced brains of any animal and
we certainly are totally ignorant of our whereabouts at birth. Nor can we get
anything but the most basic navigation information by staring at the sky. But
birds with their great visual sense learn to use the visual cues they receive
throughout their lives, guided by their own exploration and following others.
It is through this learning process that birds gain the knowledge to navigate.
Not only for navigation but they learn to use the visual features of their environment to
help them maintain a database of food availability, nesting sites and materials
and where to find mates. Very much the same as we do.

Additional information on aircraft navigation systems:

Inertial Navigation Systems

Inertial navigation systems were developed before GPS for
oceanic navigation. They consist of sets of very sensitive gyroscopes rotating
at high rpm. By measuring the precession of the gyros movement can be detected.
The pilots enter the exact location of the parking bay at the departure airport
and the motion of the aircraft as it flies across the world detected by the
gyros is converted into navigation information. This is a dead reckoning procedure
so the pilots use radio navigation information to update their positions from
time to time and for the approach and landing at the destination. These days’
fibre optic gyros are used instead of traditional gyros as they are lighter, use less power and are more
precise.

Global Positioning Systems

Global Positioning System or GPS as it is more widely known,
is in concept not much different to the celestial navigation used by Captain
Cook. It just uses round position lines instead of angular position lines to
fix the position. GPS uses a constellation of satellites and is dependent on
very accurate UTC and the ability to measure time in incredibly small
increments.

Like everything, both of these navigation systems have their
pros and cons. Inertial navigation is a self-contained system. GPS
doesn’t have the accuracy and guaranteed availability to be used solely for
navigation. GPS, as well as relying on a satellite constellation that can fail,
be interfered with or even switched off.

Radio Navigation Systems

Radio navigation uses a number of different types of radio
equipment both on the ground and in the air and is still the most common
approach and landing navigation aid. Automatic landing systems used at major
airports still rely on radio navigation equipment. However, enhanced GPS
corrected by a accurate land based survey site will, in the not to distant
future, be so accurate that all the jets arriving at an airport runway will be
able to do a blind touch down on the runway on the same tyre prints as the
other aircraft before it. And with a software program you could set up a
automatic blind landing approach in any where in the world.